The present invention relates generally to the field of implantable medical devices, and more particularly to an apparatus and method for testing an implantable medical device, such as an implantable cardioverter defibrillator (ICD), following its implant into a patient and guiding the setting of its sensing parameters.
An implantable cardioverter defibrillator (ICD) provides therapies for maintaining and restoring normal cardiac rhythms by cardiac pacing or by delivering electrical shock therapy for cardioverting or defibrillating the heart. The ICD is implanted under the skin of the user, and one or more electrical leads connected to the ICD are inserted into or in proximity to the heart of the patient. The leads carry current from the ICD to the heart tissue to stimulate the heart using either low energy pacing pulses or high-energy cardioversion/defibrillation shocks. The leads are also used for sensing electrogram (EGM) signals from the heart that are used by the ICD to determine a therapy to be delivered.
Within the ICD, sense amplifiers coupled to the leads amplify the EGM signals from the electrodes. The amplified EGM signal is then filtered, rectified, and level-detected to sense intrinsic depolarizations of the atria (referred to as P-waves) and the ventricles (referred to as R-waves).
Single chamber ICDs use a single lead placed in the right ventricle to treat ventricular arrhythmia. Dual chamber ICDs treat ventricular arrhythmia (and in some cases atrial arrhythmia as well), and have one lead placed in the right ventricle and a second lead placed in the right atrium. In some cases, a third lead may be placed to stimulate the left ventricle (e.g., in the coronary sinus).
For dual chamber detection algorithms in ICDs, the ICD delivers a therapy based upon the sensed P-waves from the atrial lead and the R-waves from the ventricular lead, which can include antitachycardia pacing (ATP), cardioversion or defibrillation. The effectiveness of the ICD in treating tachyarrhythmia depends upon the ability to accurately sense P-waves and R-waves with the atrial and ventricular leads, respectively.
During the implant of an ICD into a patient, it is common to test the ICD and its respective sensor leads and electrodes. This is generally accomplished by inducing a cardiac episode, such as ventricular fibrillation (VF), in the patient and monitoring the patient and the ICD to determine if the ICD properly detects the cardiac episode. In some patients, however, spontaneous cardiac episodes are characterized by very small amplitudes, unlike those of induced cardiac episodes. Thus, it is helpful to confirm operability at a lower sensitivity setting than the ICD's default setting.
Additionally, the implanted electrodes are at their most sensitive immediately following their initial implant. This results because tissue grows over the implanted electrodes soon after their implant, which changes the frequency content and/or amplitude of the sensed EGM signal.
Thus, during the initial testing of the ICD, it is common to reprogram the ICD to have a lower sensitivity setting than its default sensitivity setting to better ensure operability in the weeks and years following implant. Unfortunately, a common user error associated with this procedure is the failure to return the sensitivity setting back to its default value. This error may result in significant undersensing of R-waves during a cardiac episode, which may in turn result in the failure or delay in detecting the episode.
Most conventional ICDs do not provide the physician with information about a safety margin for a particular sensitivity setting. Rather, the physician is left to review the large quantity of recorded EGM data when trying to select a sensitivity setting that best prevents both undersensing and oversensing.
Accordingly, a need exists for an improved apparatus and method for testing the operability and sensitivity settings of an ICD.